Everyone is using OpenJDK these days, nobody in their right mind would pay for their licensing.
You are right, get legal advice, the cost can be passed on to them anyway.
AIUI, your costs can't (or couldn't) generally be passed on when using the small claims system. Has that changed? It's been a while since I went through the process, so it's possible that my information here is out of date.
There is obviously a personal data angle here. There might also be a defamation angle if the system works as implied by TFS, since it appears that someone's reputation has been affected because someone else lied about them and this has demonstrably caused harm? If there was more than one relevant incident then there might also be a harassment angle.
Please be careful with that advice about requesting compensation in a Letter Before Action, though. There are fairly specific rules for what you can and can't claim under our system and just going in with claiming some arbitrary figure of a few thousand pounds in "compensation" for vague damages is far from guaranteed to get the result you're hoping for. If someone were serious about challenging this kind of behaviour, they might do better to consult with a real lawyer initially to understand what they might realistically achieve and what kinds of costs and risks would be involved.
The free market works on it's own
The planet may disagree though.
A plumber can make art while plumbing. A truck driver can make art while driving. Yet that is not the first purpose of their jobs. Hence, in general, a truck driver is not an artist. Of course, nothing prevents a truck driver from being an artist.
Same for engineering (software here). Our job is to build / maintain systems. Not to create art. Now, we can create art in the process, of course, just like everyone else. But no, engineering is not art by any stretch of the imagination.
Art: the expression or application of human creative skill and imagination, typically in a visual form such as painting or sculpture, producing works to be appreciated primarily for their beauty or emotional power.
Engineering is an activity that has a practical goal: Build a plane, make a website, make this piece of code scale. Not activities primarily appreciated for their beauty or emotional power.
If your program will be up for days (think a server, a browser, etc...), the startup time can easily become negligible.
Well, each thread uses its own buffer, so there is no issue, is there ? They can then switch buffers when they feel the need to.
Engineering is inherently a creative job, so is researcher, and many others. That does not make it art.
Java is slow to start, because the JVM is a beast that takes its sweet time to get up to speed. After this hit, the type of code you are talking about will be about 5 to 10 % slower, which might be acceptable or not depending of your requirements and the value you put in all that Java provides and C does not.
The reason so few games are written in Java is that the GUI layer is not efficient to optimize your UI down to your graphic chipset *and* the fact that a full GC will stop the world fr a split second and you have no control over it. So, a game needs fluid interface which the GC doesn't allow and lightning fast graphics performance which java is not equipped for. The general CPU performance of Java is not at all an issue there.
Rust do not allow you to share a buffer between two threads for example. That might be one optimization that the C code does and the Rust implementation *cannot* do. It might not just be the ASM produced by the compiler.
That's one example of course.
What's the difference between a computer salesman and a used car salesman? A used car salesman knows when he's lying.